1. Field of the Invention
The present invention relates to a binder composition for a magnetic recording medium. More particularly, the present invention relates to a binder composition for a magnetic recording medium containing a binder resin that is suited to the manufacturing of magnetic recording media having good electromagnetic characteristics.
The present invention further relates to a magnetic recording medium containing the above binder resin.
2. Discussion of the Background
In particulate magnetic recording media, the binder plays important roles with respect to electromagnetic characteristics.
Vinyl chloride resin, polyurethane resin, polyester resin, acrylic resin, and various other resins are employed as binders in magnetic recording media. Of these, vinyl polymers such as vinyl chloride resin and acrylic resin are widely employed due to the high degree of unit freedom, ease of conducting the synthesis reaction, and the like they afford (see Document 1: Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-67855; Document 2: Japanese Unexamined Patent Publication (KOKAI) No. 2004-295926; and Document 3: Japanese Unexamined Patent Publication (KOKAI) Heisei No. 6-111277, which are expressly incorporated herein by reference in their entirety).
In addition to using microparticulate magnetic material, increasing the smoothness of the magnetic layer surface by dispersing microparticulate magnetic material to a high degree is an effective way of achieving high-density recording in the field of magnetic recording. Further, increasing the dispersion of the nonmagnetic powder contained in the nonmagnetic layer positioned beneath the magnetic layer is an effective way to increase the smoothness of the magnetic layer surface. Accordingly, the introduction of adsorptive functional groups (polar groups) such as SO3Na groups into the binders of magnetic recording media is widely practiced. However, when the quantity of polar groups introduced into the binder is increased to increase dispersion of the microparticulate powder, there is a risk of association between polar groups conversely causing a decrease in dispersion. Accordingly, it becomes difficult to ensure adequate dispersion by simply introducing polar groups. That is, it is difficult to achieve higher density recording by simply introducing polar groups into conventional vinyl polymers, including the polymers described in Documents 1 to 3.